The inventive concept relates generally to electronic memory technologies. More particularly, the inventive concept relates to variable resistance memory devices and related methods of operation.
Semiconductor memory devices can be roughly divided into two categories according to whether they retain stored information when disconnected from power. These categories include volatile memory devices, which lose stored information when disconnected from power, and nonvolatile memory devices, which retain stored information when disconnected from power.
Among nonvolatile memory devices, flash memory has achieved popularity in recent years due to attractive features such as relatively high performance and storage capacity, relatively low cost and power consumption, and an ability to withstand physical shock. Nevertheless, there is a continuing demand for flash memory devices and other forms of nonvolatile memory having even greater integration density and storage capacity. Consequently, in an effort to address this demand, researchers are continually investigating new types of nonvolatile memory devices and improving existing nonvolatile memory devices.
Examples of nonvolatile memory that have been proposed as potential alternatives to flash memory include a ferroelectric random access memory (FRAM) using a ferroelectric capacitor, a magnetic RAM (MRAM) using a tunneling magneto-resistive (TRM) film, a phase change memory device using chalcogenide alloys, and a resistive RAM (RRAM) using a variable resistance material as a data storing medium.
In an RRAM, the variable resistance material film may exhibit reversible resistance variation according to a polarity or a magnitude of an applied electrical pulse. In general, a variable resistance element, such as the variable resistance material film, can be classified as a unipolar element or a bipolar element according to a polarity of a write pulse used to program it. In a unipolar variable resistance element, a polarity of a “set pulse” may be substantially identical to that of a “reset pulse”. In a bipolar variable resistance element, a polarity of a set pulse may be opposite to that of a reset pulse.
RRAM is considered to have the potential for relatively high speed, data storage capacity, and other attractive performance characteristics. Accordingly, RRAM continues to be the subject of significant research and development.